Solid State Buffer - SSB.V1

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tortugaranger

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Solid State Buffer - SSB.V1
« on: 5 Jun 2018, 08:33 pm »
We're getting close to releasing a new product, a solid state buffer, probably towards mid/late July. We have at least 1 more prototype cycle to go through but probably 2 by the time it's all done.

This will be a variation on the solid state buffer stage used in our TPB.V1 Tube Preamp Buffer but will likely use a JFET rather than a MOSFET as the single buffer transistor. It will use the same regulated constant current source as the TPB.V1.  Since there's no tube input stage we had to add input coupling caps and bias the JFET inputs. When you distill it all down, this is a remarkably simple yet highly effecitve design that has impressed me to no end in our most recent listening tests. I'm really really excited about this buffer.

We'll likely offer this as a stand-alone buffer product but also incorporate it into our line of LDR preamps since it's small enough to fit within our existing enclosure next to the V25 preamp controller board. The buffered version of the LDR preamps will be a separate product probably referred to as a LDR Buffered Preamp to distinguish them from our LDR Passive Preamps.

More on all of this as the buffer is closer to release.


WC

Re: Solid State Buffer - SSB.V1
« Reply #1 on: 7 Jun 2018, 04:14 pm »
So will it be sold as an assembled card, unassembled, or partially assembled? Seeing as how there are 3 solder locations for the coupling caps would there be choices in caps or do we provide our own? Everything is through hole soldering.

tortugaranger

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Re: Solid State Buffer - SSB.V1
« Reply #2 on: 7 Jun 2018, 08:19 pm »
So will it be sold as an assembled card, unassembled, or partially assembled? Seeing as how there are 3 solder locations for the coupling caps would there be choices in caps or do we provide our own? Everything is through hole soldering.

Have not made a decision on selling this as an unassembled kit yet. :scratch:

It will definitely be sold as a stand alone assembled board. Yes, it's been laid out with an eye towards accommodating a wide variety of output coupling caps which can get quite large and crazy expensive. An earlier version had a mix of through hole and surface mount but decided to go 100% through hole to allow for greater flexibility in part selection.

The electrolytics will all be Elna Silmic II's, the stock coupling caps will be Vishay/Roederstein polypropylene, and the resistors will all be Vishay/Dale.  :thumb:

Ric Schultz

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Re: Solid State Buffer - SSB.V1
« Reply #3 on: 7 Jun 2018, 08:31 pm »
Looks like a simple single ended jfet buffer (the Pass B1?).  However, if you run it on plus and minus voltage then you can run it DC with no coupling caps on the input or output.  I have been using this circuit for years as a buffer......you do need to match the fets to get 0dc offset, but easy to do.  It still is a great sounding circuit, even with coupling caps. 

tortugaranger

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Re: Solid State Buffer - SSB.V1
« Reply #4 on: 8 Jun 2018, 01:53 pm »
Looks like a simple single ended jfet buffer (the Pass B1?).  However, if you run it on plus and minus voltage then you can run it DC with no coupling caps on the input or output.  I have been using this circuit for years as a buffer......you do need to match the fets to get 0dc offset, but easy to do.  It still is a great sounding circuit, even with coupling caps.

Not familar with Pass B1 but this design does not use matched pairs of JFETs but instead uses a constant current regulator. Also, until recently we used a MOSFET and am evaluating JFETs which seem to provide a bit of performance advantage. Yes, we built a zero offset prototype buffer as well for the very reason of eliminating the caps. The challenge with DC coupled preamps is how to protect against a big DC offset bump due to any number of reasons including DC inputs and possible power supply failures. I'm ok with this risk exposure for my own personal use but not for a commercial product. Adding DC offset detection and protection complicates the design considerably. Also looked at a servo design for active offset zeroing and that gets even more complex. Been around the track on all of that several times. In the end, I decided to keep it simple and safe which means coupling caps. But as you said, it still sounds great.   :thumb:

who?me?

Re: Solid State Buffer - SSB.V1
« Reply #5 on: 8 Jun 2018, 05:01 pm »
“The buffered version of the LDR preamps will be a separate product probably referred to as a LDR Buffered Preamp to distinguish them from our LDR Passive Preamps. ”

Sounds interesting, but what is the difference in sound quality between the LDR buffered preamp and the LDR passive preamp?


tortugaranger

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Re: Solid State Buffer - SSB.V1
« Reply #6 on: 8 Jun 2018, 06:03 pm »
“The buffered version of the LDR preamps will be a separate product probably referred to as a LDR Buffered Preamp to distinguish them from our LDR Passive Preamps. ”

Sounds interesting, but what is the difference in sound quality between the LDR buffered preamp and the LDR passive preamp?

The answer is a very unsatisfying "it depends" but that's the right answer.

Let's say you have a source (for ex. a DAC) with a robust output stage (as good as this buffer! ) feeding into a passive preamp which serves as a volume voltage divider of that signal.  Adding a buffer is unlikely to improve the sonics since you already have a powerful source.

On the other hand, if your source has a so-so output stage connected to passive preamp then the sound quality may benefit from a buffer that can deliver a more powerful signal. By powerful I don't mean louder (higher voltage) but a voltage signal with plenty of current supply such that there's little or no voltage droop regardless of the signal (big bass slams for instance).

Not all sources are created equal. In my view many manufacturers of DACs, CD transports, Phono stages, tuners etc. assume that there will be a nice robust preamp downstream to stiffen up the audio signal so why "overdesign" the output stage of the source. I think this is why there's such a wide variation in peoples' experience with passive preamps. Adding in a buffer usually overcomes the shortcomings of a lesser source. Or you can just blame it on the passive preamp.

I recommend a buffer vs. a full blown active preamp because in 95+% of cases you don't need the gain stage of a typical active preamp. A truly simple and effective buffer gets the job done with the least number of components and shortest signal path which more often than not results in a better sounding system with less noise.

Sure, there are also potential impedance bridging issues if the effective impedance of the passive || amp is too low but I've found that to be far less common a problem than all the attention it gets.

In short, if you're using a passive attenuator, weak sources benefits from a buffer,  strong sources don't need a buffer.

WC

Re: Solid State Buffer - SSB.V1
« Reply #7 on: 24 Aug 2018, 02:38 pm »
Since the buffered preamp is getting closer to shipping, have you given any further thought as to how/when you were going to offer the buffer board?

tortugaranger

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Re: Solid State Buffer - SSB.V1
« Reply #8 on: 27 Aug 2018, 02:25 pm »
Since the buffered preamp is getting closer to shipping, have you given any further thought as to how/when you were going to offer the buffer board?

The when is probably starting later in September or into October. We need to get the production up and going (starting later this week) for the buffer boards used in our new LDR300 model and depending on how that goes we'll decide on when to start offering the SSB.V1 Buffer Board. The SSB.V1 is straight forward enough that most will be able to assemble it from "parts in a bag" but we still need to make a decision whether we want to support a "parts in a bag" approach vs. only sell it fully assembled and tested. We need a little more time with that question.